Analysis of failed/damaged LPTR blades of an aeroengine

The LPTR blade XA 9799-09 had failed by fatigue. The fatigue crack had initiated at the leading edge at a distance of about 8 mm from the blade root platform and propagated progressively over a period of time before culminating in overload failure. It appears most probable that the fatigue crack had initiated due to the presence of cracks in the coating caused by mechanical damage. The mechanical damage appears to have occurred either during post coating grinding or handling. The blade XA 9799-17 had failed by impact subsequent to the primary fatigue failure of blade XA 9799-09. The microstructure and the coating thickness of the failed blades were found satisfactory. Examination of unused blades revealed grinding marks, deep scratch marks and dent marks at the leading and trailing edges. There were no cracks in the coating of these blades